U.S. patent number 8,111,035 [Application Number 11/946,362] was granted by the patent office on 2012-02-07 for charging system, charging device and battery pack.
This patent grant is currently assigned to Panasonic Corporation. Invention is credited to Jun Asakura, Yoshio Nakatani, Hajime Nishino.
United States Patent |
8,111,035 |
Nishino , et al. |
February 7, 2012 |
Charging system, charging device and battery pack
Abstract
A charging system is provided with a secondary battery, a
charging current supplier for supplying a charging current to the
secondary battery, an internal resistance detector for detecting
the resistance value of the internal resistance of the secondary
battery, and a charge controller for increasing the charging
current to be supplied to the secondary battery by the charging
current supplier as the resistance value detected by the internal
resistance detector decreases.
Inventors: |
Nishino; Hajime (Osaka,
JP), Asakura; Jun (Osaka, JP), Nakatani;
Yoshio (Osaka, JP) |
Assignee: |
Panasonic Corporation (Osaka,
JP)
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Family
ID: |
39462977 |
Appl.
No.: |
11/946,362 |
Filed: |
November 28, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080122399 A1 |
May 29, 2008 |
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Foreign Application Priority Data
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Nov 29, 2006 [JP] |
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2006-322141 |
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Current U.S.
Class: |
320/103; 429/89;
307/46; 320/107; 320/112; 307/64; 307/66 |
Current CPC
Class: |
H02J
7/0069 (20200101); H02J 7/0091 (20130101); H02J
7/0031 (20130101); H02J 7/007194 (20200101) |
Current International
Class: |
H02J
7/00 (20060101); H02J 1/12 (20060101); H01M
2/12 (20060101) |
Field of
Search: |
;320/103 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2389376 |
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Jul 2000 |
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CN |
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5-111184 |
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Apr 1993 |
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JP |
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6-78471 |
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Mar 1994 |
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JP |
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8-098426 |
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Apr 1996 |
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JP |
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8-163788 |
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Jun 1996 |
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JP |
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09-084277 |
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Mar 1997 |
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JP |
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Other References
Japanese Notice of Reasons for Rejection, w/ English translation
thereof, issued in Japanese Patent Application No. JP 2006-322141
dated Sep. 7, 2010. cited by other .
Chinese Office Action, w/ English translation thereof, issued in
Chinese Patent Application No. CN 200710194670.1 dated Mar. 3,
2011. cited by other.
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Primary Examiner: Fantu; Yalkew
Attorney, Agent or Firm: McDermott Will & Emery LLP
Claims
What is claimed is:
1. A charging system, comprising: a secondary battery; a charging
current supplier for supplying a charging current to the secondary
battery; an internal resistance detector for detecting a resistance
value of the internal resistance of the secondary battery; a charge
controller for increasing the charging current to be supplied to
the secondary battery by the charging current supplier as the
resistance value detected by the internal resistance detector
decreases; a voltage detector for detecting a terminal voltage of
the secondary battery; and a current detector for detecting the
current flowing into the secondary battery, wherein the internal
resistance detector calculates the resistance value of the internal
resistance by dividing a difference between the terminal voltage
detected by the voltage detector when the charging current supplier
supplies a specified first internal resistance detection current to
the secondary battery and the terminal voltage detected by the
voltage detector when the charging current supplier supplies a
specified second internal resistance detection current different
from the first internal resistance detection current by a
difference between the first internal resistance detection current
and the second internal resistance detection current.
2. A charging system according to claim 1, wherein the charge
controller causes the charging current supplier to supply the
current to the secondary battery such that a product of the square
of the current value of the charging current to be supplied to the
secondary battery by the charging current supplier and the
resistance value detected by the internal resistance detector
becomes a specific value set beforehand.
3. A charging system according to claim 1, wherein the charge
controller causes the charging current supplier to supply the
current to the secondary battery such that a product of the current
value of the charging current to be supplied to the secondary
battery by the charging current supplier and the resistance value
detected by the internal resistance detector becomes a specific
value set beforehand.
4. A charging system according to claim 1, further comprising: a
voltage detector for detecting a terminal voltage of the secondary
battery; and a constant voltage charging section for causing the
charging current supplier to supply a current for the charging so
that, when the terminal voltage detected by the voltage detector
increases to or above a preset final voltage, the secondary battery
is charged with a constant voltage through the application of the
final voltage.
5. A charging system according to claim 3, further comprising: a
constant voltage charging section for causing the charging current
supplier to supply a current for the charging so that, when the
terminal voltage detected by the voltage detector increases to or
above a preset final voltage, the secondary battery is charged with
a constant voltage through the application of the final
voltage.
6. A charging system according to claim 2, further comprising: a
constant voltage charging section for causing the charging current
supplier to supply a current for the charging so that, when the
terminal voltage detected by the voltage detector increases to or
above a preset final voltage, the secondary battery is charged with
a constant voltage through the application of the final
voltage.
7. A charging system, comprising: a secondary battery; a charging
current supplier for supplying a charging current to the secondary
battery; an internal resistance detector for detecting a resistance
value of the internal resistance of the secondary battery; and a
charge controller for increasing the charging current to be
supplied to the secondary battery by the charging current supplier
as the resistance value detected by the internal resistance
detector decreases; a state of charge detector for detecting a
state of charge SOC of the secondary battery; a storage for storing
the state of charge SOC of the secondary battery and the resistance
value of the internal resistance in correspondence with each other;
a voltage detector for detecting a terminal voltage of the
secondary battery; and a constant voltage charging section for
causing the charging current supplier to supply a current for the
charging so that, when the terminal voltage detected by the voltage
detector increases to or above a preset final voltage, the
secondary battery is charged with a constant voltage through the
application of the final voltage, wherein the internal resistance
detector obtains the resistance value stored in the storage in
correspondence with the state of charge SOC of the secondary
battery detected by the state of charge detector as the resistance
value of the internal resistance of the secondary battery; and the
charge controller causes the charging current supplier to supply
the current to the secondary battery such that a product of the
current value of the charging current to be supplied to the
secondary battery by the charging current supplier and the
resistance value detected by the internal resistance detector
becomes a specific value set beforehand.
8. A charging system, comprising: a secondary battery; a charging
current supplier for supplying a charging current to the secondary
battery; an internal resistance detector for detecting a resistance
value of the internal resistance of the secondary battery; and a
charge controller for increasing the charging current to be
supplied to the secondary battery by the charging current supplier
as the resistance value detected by the internal resistance
detector decreases; a state of charge detector for detecting a
state of charge SOC of the secondary battery; a storage for storing
the state of charge SOC of the secondary battery and the resistance
value of the internal resistance in correspondence with each other;
a voltage detector for detecting a terminal voltage of the
secondary battery; and a constant voltage charging section for
causing the charging current supplier to supply a current for the
charging so that, when the terminal voltage detected by the voltage
detector increases to or above a preset final voltage, the
secondary battery is charged with a constant voltage through the
application of the final voltage, wherein the internal resistance
detector obtains the resistance value stored in the storage in
correspondence with the state of charge SOC of the secondary
battery detected by the state of charge detector as the resistance
value of the internal resistance of the secondary battery; and the
charge controller causes the charging current supplier to supply
the current to the secondary battery such that a product of the
square of the current value of the charging current to be supplied
to the secondary battery by the charging current supplier and the
resistance value detected by the internal resistance detector
becomes a specific value set beforehand.
9. A charging device, comprising: a connection terminal for the
connection with a secondary battery, a charging current supplier
for supplying a current for charging the secondary battery to the
connection terminal; an internal resistance detector for detecting
a resistance value of the internal resistance of the secondary
battery connected with the connection terminal; a charge controller
for increasing the current to be supplied to the connection
terminal by the charging current supplier as the resistance value
detected by the internal resistance detector decreases; a voltage
detector for detecting a terminal voltage of the secondary battery;
and a current detector for detecting the current flowing into the
secondary battery, wherein the internal resistance detector
calculates the resistance value of the internal resistance by
dividing a difference between the terminal voltage detected by the
voltage detector when the charging current supplier supplies a
specified first internal resistance detection current to the
secondary battery and the terminal voltage detected by the voltage
detector when the charging current supplier supplies a specified
second internal resistance detection current different from the
first internal resistance detection current by a difference between
the first internal resistance detection current and the second
internal resistance detection current.
10. A battery pack to be connected with a charging device for
outputting a current for charging a secondary battery in response
to an external instruction, comprising: a secondary battery; an
internal resistance detector for detecting a resistance value of
the internal resistance of the secondary battery; and a charge
controller for charging the secondary battery by outputting the
instruction to the charging device so that a current to be supplied
to the secondary battery by the charging device is increased as the
resistance value detected by the internal resistance detector
decreases; a voltage detector for detecting a terminal voltage of
the secondary battery; and a current detector for detecting the
current flowing into the secondary battery, wherein the internal
resistance detector calculates the resistance value of the internal
resistance by dividing a difference between the terminal voltage
detected by the voltage detector when the charging current supplier
supplies a specified first internal resistance detection current to
the secondary battery and the terminal voltage detected by the
voltage detector when the charging current supplier supplies a
specified second internal resistance detection current different
from the first internal resistance detection current by a
difference between the first internal resistance detection current
and the second internal resistance detection current.
Description
CLAIM OF PRIORITY
This application claims the benefit of Japanese Patent Application
No. JP 2006-322141, filed on Nov. 29, 2006, the disclosure of which
is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charging system and a charging
device for charging a secondary battery and a battery pack provided
with a secondary battery.
2. Description of the Background Art
FIG. 6 is a chart showing an operation of charging a secondary
battery by a constant-current, constant-voltage (CCCV) charging
according to a background part. FIG. 6 shows a closed circuit
voltage CCV of the secondary battery, an open circuit voltage OCV
of the secondary battery, a charging current Ic, a state of charge
SOC of the secondary battery and an internal resistance Ri of the
secondary battery in the case of charging the secondary battery,
e.g. a lithium ion battery. FIG. 7 is a conceptual diagram showing
an equivalent circuit of a secondary battery 100.
The equivalent circuit of the secondary battery 100 shown in FIG. 7
is represented by a series circuit of a voltage source E and the
internal resistance Ri. Then, the closed circuit voltage CCV is
equivalent to voltages at the opposite ends of the series circuit
of the voltage source E and the internal resistance Ri, and the
open circuit voltage OCV is equivalent to voltages at the opposite
ends of the voltage source E. The secondary battery 100 may be
assembled cells in which, for example, a plurality of unit cells of
a lithium ion battery are connected in series parallel.
In CCCV charging, charging by constant current I2 is first carried
out. In constant current discharge of one hour, the current level
that can discharge electricity assumes a nominal capacity NC "1C".
Then, the electric current which multiplied number P of the cells
arranged in parallel by 70% of the electric current of the "1C" is
I2. In this way, the constant current I2 is charged.
When the closed circuit voltage CCV reaches a final voltage Vf
(.times.the number of the cells arranged in series), a transition
is made to a constant voltage (CV) charging area and the charging
current Ic is decreased so as not to exceed the final voltage Vf
(.times.the number of the cells arranged in series). When the
charging current Ic is decreased to a current value I3 set
according to temperature, full charging is judged and the supply of
the charging current is stopped. The above charging control method
can be read, for example, from Japanese Unexamined Patent
Publication No. H06-78471.
In such CCCV charging, the maximum value of the charging current Ic
is the current I2 flowing into the secondary battery 100 during the
constant current (CC) charging from the start to the end of the
charging.
The internal resistance Ri of the battery is a sum of reaction
resistance, which results from movements of electric charges caused
by the chemical reaction in the battery, and electronic resistance,
which is resistance of electrolyte and electrodes. In the secondary
battery 100, e.g. the lithium ion battery, if a state of charge SOC
(hereinafter, merely "SOC") is low, an active material on the outer
surfaces of the electrodes contracts to increase electronic
resistance. If the SOC is high, the active material on the outer
surfaces of the electrodes expands to reduce electronic resistance.
Thus, the internal resistance Ri has a property of becoming larger
as the SOC decreases while becoming smaller as charging proceeds to
increase the SOC.
Then, at an initial stage of the charging where the constant
current (CC) charging was started, the current I2 flows through the
internal resistance Ri when the active material contracts to
maximize the internal resistance Ri. Thus, a voltage drop by the
internal resistance Ri increases. Since the closed circuit voltage
CCV is a sum of the open circuit voltage OCV and the voltage drop
by the internal resistance Ri, a difference between the open
circuit voltage OCV and the closed circuit voltage CCV is largest
at the initial stage of the charging and becomes gradually smaller
as the charging proceeds to decrease the internal resistance Ri. It
is possible to think of the internal resistance Ri while dividing
it into an internal resistance Rim caused at the negative electrode
side of the secondary battery 100 and an internal resistance Rip
caused at the positive electrode side.
FIG. 8 is a chart showing the open circuit voltage OCV, the closed
circuit voltage CCV and a relationship of potentials at the
positive and negative electrodes with respect to a lithium
reference. In FIG. 8, a voltage V1 represents a voltage drop caused
by the flow of the charging current Ic through the internal
resistance Rim at the negative electrode side, wherein
V1=Rim.times.Ic. Further, a voltage V2 represents a voltage drop
caused by the flow of the charging current Ic through the internal
resistance Rip at the positive electrode side, wherein
V2=Rip.times.Ic.
Here, if the internal resistance Ri is zero, i.e. the internal
resistance Rim is zero at the start of the charging, i.e. in a
state where the SOC is substantially zero, the closed circuit
voltage CCV is equal to the open circuit voltage OCV and the
negative electrode potential with respect to the lithium reference
takes a positive value larger than 0 V. However, the internal
resistance Ri is actually not zero and, accordingly,
CCV=OCV+V1+V2=OCV+Rim.times.Ic+Rip.times.Ic. Then, the negative
electrode potential of the secondary battery 100 is decreased by
V1=Rim.times.Ic. Here, since Rim increases because the SOC is
lowest at the start of the charging and the charging current Ic is
the maximum current I2 from the start to the end of the charging by
the constant current (CC) charging, there is a likelihood that V1
is also maximized from the start to the end of the charging and the
negative electrode voltage of the secondary battery 100 falls to or
below 0 V. If the negative electrode voltage falls to or below V,
there has been a problem that lithium precipitates at the negative
electrode to deteriorate the secondary battery 100.
SUMMARY OF THE INVENTION
In view of the above situation, an object of the present invention
is to provide a charging system, a charging device and a battery
pack capable of reducing a likelihood of deteriorating a secondary
battery due to the internal resistance of the secondary
battery.
One aspect of the present invention is directed to a charging
system, comprising a secondary battery; a charging current supplier
for supplying a charging current to the secondary battery; an
internal resistance detector for detecting the resistance value of
the internal resistance of the secondary battery; and a charge
controller for increasing the charging current to be supplied to
the secondary battery by the charging current supplier as the
resistance value detected by the internal resistance detector
decreases.
According to this construction, the charging current is increased
as the internal resistance of the secondary battery decreases, and
the charging current is decreased as the internal resistance
increases. Then, if the internal resistance of the secondary
battery is large as at an initial stage of the charging, the
charging current is decreased to reduce a voltage drop and self
heat generation caused by the internal resistance of the secondary
battery, with the result that a likeliness of deteriorating the
secondary battery due to the internal resistance of the secondary
battery can be reduced. Further, since the charging current can be
increased as the charging proceeds to decrease the internal
resistance, it becomes easier to suppress the extension of the
charging time and shorten the charging time by increasing the
charging current.
Another aspect of the present invention is directed to a charging
device, comprising a connection terminal for the connection with a
secondary battery; a charging current supplier for supplying a
current for charging the secondary battery to the connection
terminal; an internal resistance detector for detecting the
resistance value of the internal resistance of the secondary
battery connected with the connection terminal; and a charge
controller for increasing the current to be supplied to the
connection terminal by the charging current supplier as the
resistance value detected by the internal resistance detector
decreases.
According to this construction, the charging current is increased
as the internal resistance of the secondary battery connected with
the connection terminal decreases while being decreased as the
internal resistance increases. Then, if the internal resistance of
the secondary battery is large as at an initial stage of the
charging, the charging current is decreased to reduce a voltage
drop and self heat generation caused by the internal resistance of
the secondary battery, with the result that a likeliness of
deteriorating the secondary battery due to the internal resistance
of the secondary battery can be reduced. Further, since the
charging current can be increased as the charging proceeds to
decrease the internal resistance, it becomes easier to suppress the
extension of the charging time and shorten the charging time by
increasing the charging current.
Still another aspect of the present invention is directed to a
battery pack to be connected with a charging device for outputting
a current for charging a secondary battery in response to an
external instruction, comprising a secondary battery; an internal
resistance detector for detecting the resistance value of the
internal resistance of the secondary battery; and a charge
controller for charging the secondary battery by outputting the
instruction to the charging device so that a current to be supplied
to the secondary battery by the charging device is increased as the
resistance value detected by the internal resistance detector
decreases.
According to this construction, in response to the instruction from
the charge controller, the charging device increases the charging
current as the internal resistance of the secondary battery
decreases while decreasing the charging current as the internal
resistance increases. Then, if the internal resistance of the
secondary battery is large as at an initial stage of the charging,
the charging current is decreased to reduce a voltage drop and self
heat generation caused by the internal resistance of the secondary
battery, with the result that a likeliness of deteriorating the
secondary battery due to the internal resistance of the secondary
battery can be reduced. Further, since the charging current can be
increased as the charging proceeds to decrease the internal
resistance, it becomes easier to suppress the extension of the
charging time and shorten the charging time by increasing the
charging current. In this case, it is sufficient for the charging
device to output the current in response to the instruction from
the battery pack, the same charging device can be used even in the
case of charging a battery pack including a secondary battery
having different characteristics.
These and other objects, features and advantages of the present
invention will become more apparent upon a reading of the following
detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing an exemplary construction of a
charging system according to one embodiment of the invention,
FIGS. 2A and 2B are charts showing an operation of an internal
resistance calculating section shown in FIG. 1, wherein FIG. 2A
shows a current flowing into a secondary battery and FIG. 2B shows
a terminal voltage of the secondary battery,
FIG. 3 is a block diagram showing a modification of the charging
system shown in FIG. 1,
FIG. 4 is a diagram showing an exemplary operation of the charging
system shown in FIG. 1,
FIG. 5 is a flow chart showing the exemplary operation of the
charging system shown in FIG. 1,
FIG. 6 is a chart showing a secondary battery charging operation by
constant-current, constant-voltage (CCCV) charging according to a
background art,
FIG. 7 is a conceptual diagram showing an equivalent circuit of the
secondary battery, and
FIG. 8 is a diagram showing an open circuit voltage OCV, a closed
circuit voltage CCV and a relationship of potentials at positive
and negative electrodes with respect to a lithium reference.
DESCRIPTION OF PREFERRED EMBODIMENTS
Hereinafter, one embodiment of the present invention is described
with reference to the accompanying drawings. It should be noted
that constructions identified by the same reference numerals in the
respective figures are the same constructions and are not
repeatedly described. FIG. 1 is a block diagram showing an
exemplary construction of a charging system according to one
embodiment of the present invention. This charging system 1
includes a battery pack 2 and a charger 3 for charging the battery
pack 2. An unillustrated load equipment to have power supplied from
the battery pack 2 may be further included to construct an
electronic equipment system which is an example of the charge
system. In such a case, the battery pack 2 charged by the charger 3
in FIG. 1 may be installed in the load equipment and charged
through the load equipment. The battery pack 2 and the charger 3 is
connected with each other by high-side terminals T11, T21 for a
direct current for power feeding, terminals T12, T22 for
communication signals and GND terminals T13, T23 for power feeding
and communication signals. Similar terminals are provided also in
the case of providing the load equipment.
A switching element 12, for example, comprised of a FET (Field
Effect Transistor), a relay switch and the like is provided in a
high-side charging path 11 for the direct current extending from
the terminal T11, and this charging path 11 is connected with a
high-side terminal of the secondary battery 14. A low-side terminal
of the secondary battery 14 is connected with the GND terminal T13
via a low-side charging path 15 for the direct current, and a
current detection resistor 16 (current detector) for converting a
charging current and a discharging current into voltage values is
provided in this charging path 15.
For example, a lithium ion secondary battery is used as the
secondary battery 14. Further, the secondary battery 14 may be
assembled cells in which a plurality of secondary batteries are
connected in series parallel.
The temperature of the secondary battery 14 is detected by a
temperature sensor 17 and inputted to an analog-to-digital (A/D)
converter 19 in a control IC 18. A terminal voltage Vb of the
secondary battery 14 is read by a voltage detection circuit 20
(voltage detector) and inputted to the analog-to-digital converter
19 in the control IC 18. Further, a current value detected by the
current detection resistor 16 is inputted to the analog-to-digital
converter 19 in the control IC 18. The analog-to-digital converter
19 converts the respective input values into digital values and
outputs them to a controller 21.
The controller 21 includes, for example, a CPU (Central Processing
Unit) for performing a specified arithmetic processing, a ROM (Read
Only Memory) storing a specified control program, a RAM (Random
Access Memory) temporarily saving data, peripheral circuits and the
like of these, and functions as a charge/discharge controlling
section 211 (charge controller), an internal resistance calculating
section 212 (internal resistance detector) and a constant voltage
charging section 213 by executing the control program stored in the
ROM.
The charge/discharge controlling section 211 calculates the voltage
value and current value instructed to be outputted from the charger
3 in response to the respective input values from the
analog-to-digital converter 19, and sends the calculated voltage
value and current value from a communicator 22 to the charger 3 via
the terminals T12, T22; T13, T23. The charge/discharge controlling
section 211 performs protection operations, for example, by
shutting off the switching element 12 based on the respective input
values from the analog-to-digital converter 19 in response to a
short circuit between the terminals T11 and T13, abnormality
outside the battery pack 2 such as an abnormal current from the
charger 3, an abnormal temperature increase of the secondary
battery 14 and the like.
Further, the charge/discharge controlling section 211 increases the
charging current Ic to be supplied to the secondary battery 14 by
the charger 3 as the internal resistance Ri of the secondary
battery 14 calculated by the internal resistance controlling
section 212 decreases.
The internal resistance controlling section 212 detects the
internal resistance Ri of the secondary battery 14. FIG. 2 are
charts showing the operation of the internal resistance controlling
section 212, wherein FIG. 2A shows a current flowing into the
secondary battery 14 and FIG. 2B shows the terminal voltage Vb of
the secondary battery 14. First, the internal resistance
controlling section 212 sends an instruction to output an internal
resistance detection current Is from the communicator 22 to the
charger 3 via the terminals T12, T22; T13, T23, and the internal
resistance detection current Is (first internal resistance
detection current) is supplied to the secondary battery 14 by the
charger 3. Subsequently, the internal resistance controlling
section 212 obtains the terminal voltage Vb of the secondary
battery 14 obtained in the analog-to-digital converter 19, i.e. a
closed circuit voltage CCV, sends an instruction to zero the
current supply of the charger 3 (corresponding to the case of
setting a second internal resistance detection current to 0 A) from
the communicator 22 to the charger 3 via the terminals T12, T22;
T13, T23, and obtains the terminal voltage Vb of the secondary
battery 14 obtained in the analog-to-digital converter 19, i.e. an
open circuit voltage OCV when the current flowing into the
secondary battery 14 is zeroed. Then, the internal resistance
controlling section 212 calculates the internal resistance Ri by
the following equation (1): Ri=(CCV-OCV)/Is (1).
In FIG. 2B, a voltage V3 generated simultaneously with a current
pulse of FIG. 2A is a voltage component resulting from electronic
resistance and a voltage component V4, which gradually changes from
a timing later than the current pulse of FIG. 2A, is a voltage
component resulting from reaction resistance.
It is sufficient to set the second internal resistance detection
current to a current value different from the first internal
resistance detection current, and the second internal resistance
detection current is not limited to 0 A. For example, if it is
assumed that Is.sub.1 denotes the first internal resistance
detection current, CCV.sub.1 the terminal voltage Vb of the
secondary battery 14 obtained in the analog-to-digital converter 19
when the first internal resistance detection current Is.sub.1 was
supplied to the secondary battery 14 and CCV.sub.2 the terminal
voltage Vb of the secondary battery 14 obtained in the
analog-to-digital converter 19 when the second internal resistance
detection current Is.sub.2 was supplied to the secondary battery
14, the internal resistance controlling section 212 may calculate
the internal resistance Ri by the following equation (2). Further,
since it is sufficient for the first and second internal resistance
detection currents Is.sub.1, Is.sub.2 to be current values
different from each other, the current value for the purpose of
pulse charging may be changed to be used as the first and second
internal resistance detection currents Is.sub.1, Is.sub.2.
Ri=|CCV.sub.1-CCV.sub.2|/Is.sub.1-Is.sub.2| (2).
In this case, it is possible to reduce a likelihood of extending a
charging time for the measurement of the internal resistance Ri
since the internal resistance Ri can be measured without zeroing
the charging current.
FIG. 2B shows an example in which the terminal voltages Vb are
obtained as the closed circuit voltage CCV and the open circuit
voltage OCV after the value of the voltage component V4 becomes
steady, i.e. after the terminal voltage Vb becomes steady following
the rise and fall of the current pulse. However, since it takes
time to stabilize a voltage, the terminal voltages Vb, for example,
upon the lapse of a preset period .DELTA.t after the rise and fall
of the current may be obtained as the closed circuit voltage CCV
and the open circuit voltage OCV before the terminal voltages Vb
reach steady values. Similarly, the terminal voltages Vb upon the
lapse of a preset period .DELTA.t after the values of the currents
to be supplied to the secondary battery 14 are changed to Is.sub.1,
Is.sub.2 may be obtained as CCV.sub.1, CCV.sub.2. In this case, the
terminal voltage Vb is detected while the voltage component V4 is
being changed. If the period .DELTA.t is set at a specific value,
the closed circuit voltage CCV and the open circuit voltage OCV
(CCV.sub.1, CCV.sub.2) obtained in this way are obtained as values
reflecting the internal resistance Ri. Therefore, the charging
current can be set based on the internal resistance Ri obtained in
this way.
A storage 215 may be further provided and a controller 21a may be
used in place of the controller 21, for example, as shown in FIG.
3. The controller 21a further functions as a state of charge
detecting section 214 for detecting the SOC of the secondary
battery 14.
The state of charge detecting section 214 calculates the SOC of the
secondary battery 14, for example, by integrating the charging
current Ic obtained in the analog-to-digital converter 19. The
storage 215 is constructed, for example, using a nonvolatile
storage element such as an EEPROM (Electrically Erasable and
Programmable Read Only Memory), and the SOC of the secondary
battery 14 and the internal resistance Ri are stored in
correspondence beforehand. An internal resistance controlling
section 212a may obtain the internal resistance Ri stored in the
storage 215 in correspondence with the SOC of the secondary battery
14 calculated by the state of charge detecting section 214 as the
internal resistance Ri of the secondary battery 14.
The constant voltage charging section 213 outputs an instruction to
stabilize the output voltage of the charger 3 at a final voltage Vf
if the terminal voltage Vb obtained in the analog-to-digital
converter 19 rises to or above the final voltage Vf set, for
example, to 4.2 V, and performs constant voltage charging by
supplying the charging current Ic by means of a charging current
supply circuit 33 in such a manner that the final voltage Vf is
applied to the secondary battery 14.
In the charger 3, the instruction from the battery pack 2 is
received by a communicator 32 as communication means in a control
IC 30, a charge controller 31 controls the charging current supply
circuit 33 (charging current supplier) to cause the charging
current Ic to be supplied with the above voltage value, current
value and pulse width. The charging current supply circuit 33 is
comprised of an AC-to-DC converter or a DC-to-DC converter,
converts the input voltage into the voltage value, current value
and pulse width instructed from the charge controller 31 and
supplies the charging current Ic to the charging paths 11, 15 via
the terminals T21, T11; T23, T13.
The control IC 18 is not limited to the one provided in the battery
pack 2, and may be provided in the charger 3.
Next, the operation of the charging system 1 constructed as above
is described. FIG. 4 is a chart showing an exemplary operation of
the charging system 1 shown in FIG. 1. FIG. 5 is a flow chart
showing the exemplary operation of the charging system shown in
FIG. 1. First, the internal resistance Ri of the secondary battery
14 is calculated by the internal resistance controlling section 212
(Step S1, timing T1).
Subsequently, a target value of the charging current Ic is so
calculated by the charge/discharge controlling section 211 that a
product of the charging current Ic and the internal resistance Ri
becomes a specific value Va set beforehand. Specifically, the
target value of the charging current Ic is given by the following
equation (3): Ic=Va/Ri (3).
Subsequently, an instruction to output the charging current Ic
given by the equation (3) is sent to the charge controller 31 by
the charge/discharge controlling section 211, and the charging
current Ic given by the equation (3) is outputted from the charging
current supply circuit 33 in accordance with a control signal from
the charge controller 31 (Step S2, timing T2).
In this case, the set value Va corresponds to a difference between
the closed circuit voltage CCV and the open circuit voltage OCV
shown in FIG. 8, i.e. Va=V1+V2. The set value Va is so set that the
negative electrode potential does not fall to or below 0V due to a
voltage drop caused at the negative electrode side of the secondary
battery 14, i.e. an excessive increase of the voltage V1.
Then, the charging current Ic flowing into the secondary battery 14
is set to the current value given by the equation (3), thereby
reducing a likelihood of decreasing the negative electrode
potential to or below 0V. As a result, there can be reduced a
likelihood of deteriorating the secondary battery 14 due to the
precipitation of lithium at the negative electrode.
Thereafter, the secondary battery 14 is charged with the charging
current Ic and the SOC and the terminal voltage Vb gradually
increase.
Subsequently, in Step S3, the charge/discharge controlling section
211 compares the final voltage Vf and the terminal voltage Vb, and
Steps S1 to S3 are repeated again unless the terminal voltage Vb
has reached the final voltage Vf (NO in Step S3) while Step S4
follows to move into constant voltage charging if the terminal
voltage Vb is equal to or above the final voltage Vf.
Since the current value of the charging current Ic is so adjusted
that the product of the charging current Ic and the internal
resistance Ri becomes the specific value Va set beforehand by the
operations in Steps S1 to S3, the likelihood that the negative
electrode voltage falls to or below 0V by charging is reduced,
which results in a reduction in the likelihood of deteriorating the
secondary battery 14 due to the precipitation of lithium at the
negative electrode. Further, by the operations of Steps S1 to S3,
the charging current Ic increases as the internal resistance Ri
decreases while decreasing as the internal resistance Ri increases.
Then, the charging current Ic is set at a small current value if
the internal resistance Ri is large at an initial stage of
charging. Thus, self heat generation caused by the flow of the
current through the internal resistance Ri is reduced, thereby
decreasing a likelihood of deteriorating the secondary battery 14
due to an excessive temperature increase by the self heat
generation. Further, since the charging current Ic can be increased
as the charging proceeds to decrease the internal resistance Ri, it
becomes easier to suppress the extension of the charging time and
shorten the charging time by increasing the charging current Ic
while reducing the likelihood of deteriorating the secondary
battery 14.
Subsequently, in Step S4, an instruction to output the final
voltage Vf is given to the charge controller 31 by the constant
voltage charging section 213, and the final voltage Vf is outputted
from the charging current supply circuit 33 in accordance with a
control signal from the charge controller 31 to start the constant
voltage charging (timing T3). Then, the final voltage Vf is applied
to the opposite ends of the secondary battery 14, and the state of
charge SOC of the secondary battery 14 gradually increases while
the charging current Ic gradually decreases.
Then, the current value of the charging current Ic obtained in the
analog-to-digital converter 19 and the current value I3 are
compared by the constant voltage charging section 213, and it is
returned to Step S4 to continue the constant voltage charging if
the charging current Ic is above the current value I3 (NO in Step
S5), whereas an instruction to zero the charging current is
outputted to the charge controller 31 by the constant voltage
charging section 213 and the output current of the charging current
supply circuit 33 is zeroed by the charge controller 31 to finish
the charging (Step S6, timing T4) if the charging current Ic is
equal to or below the current value I3 (YES in Step S5).
It should be noted that the charge/discharge controlling section
211 may calculate the target value of the charging current Ic so
that a product of the square of the charging current Ic and the
internal resistance Ri becomes a specific value Wa set beforehand
in Step S2. In this case, the charging current Ic is given by a
square root of (Wa/Ri). The product of the square of the charging
current Ic and the internal resistance Ri is power consumption in
the internal resistance Ri. The set value Wa is set to such a value
as not to deteriorate the internal resistance Ri by the self heat
generation.
If the charging current Ic is so adjusted that the product of the
square of the charging current Ic and the internal resistance Ri,
i.e. the self heat generation of the internal resistance Ri becomes
the specified set value Wa in Steps S1 to S3, the likelihood of
deteriorating the secondary battery 14 by an excessive temperature
increase caused by the self heat generation of the internal
resistance Ri is reduced. Further, since the charging current Ic
can be increased as the charging proceeds to decrease the internal
resistance Ri, it becomes easier to suppress the extension of the
charging time and shorten the charging time by increasing the
charging current Ic while reducing the likelihood of deteriorating
the secondary battery 14.
A charging system according to one aspect of the present invention
comprises a secondary battery; a charging current supplier for
supplying a charging current to the secondary battery; an internal
resistance detector for detecting the resistance value of the
internal resistance of the secondary battery; and a charge
controller for increasing the charging current to be supplied to
the secondary battery by the charging current supplier as the
resistance value detected by the internal resistance detector
decreases.
According to this construction, the charging current is increased
as the internal resistance of the secondary battery decreases, and
the charging current is decreased as the internal resistance
increases. Then, if the internal resistance of the secondary
battery is large as at an initial stage of the charging, the
charging current is decreased to reduce a voltage drop and self
heat generation caused by the internal resistance of the secondary
battery, with the result that a likeliness of deteriorating the
secondary battery due to the internal resistance of the secondary
battery can be reduced. Further, since the charging current can be
increased as the charging proceeds to decrease the internal
resistance, it becomes easier to suppress the extension of the
charging time and shorten the charging time by increasing the
charging current.
The charge controller preferably causes the charging current
supplier to supply the current to the secondary battery such that a
product of the current value of the charging current to be supplied
to the secondary battery by the charging current supplier and the
resistance value detected by the internal resistance detector
becomes a specific value set beforehand.
According to this construction, the current to be supplied to the
secondary battery is so adjusted that the product of the current to
be supplied to the secondary battery and the internal resistance of
the secondary battery, i.e. a voltage drop caused by the internal
resistance of the secondary battery becomes the specific set value.
Thus, a likelihood of deteriorating the secondary battery by an
excessive voltage drop caused by the internal resistance of the
secondary battery can be reduced.
The charge controller may cause the charging current supplier to
supply the current to the secondary battery such that a product of
the square of the current value of the charging current to be
supplied to the secondary battery by the charging current supplier
and the resistance value detected by the internal resistance
detector becomes a specific value set beforehand.
According to this construction, the current to be supplied to the
secondary battery is so adjusted that the product of the square of
the current to be supplied to the secondary battery and the
internal resistance of the secondary battery, i.e. the power
consumption by the internal resistance of the secondary battery
becomes the specific set value. Thus, a likelihood of deteriorating
the secondary battery by excessive heat generation caused by the
internal resistance of the secondary battery can be reduced.
It is preferable that a voltage detector for detecting a terminal
voltage of the secondary battery and a current detector for
detecting the current flowing into the secondary battery are
further provided; and the internal resistance detector calculates
the resistance value of the internal resistance by dividing a
difference between the terminal voltage detected by the voltage
detector when the charging current supplier supplies a specified
first internal resistance detection current to the secondary
battery and the terminal voltage detected by the voltage detector
when the charging current supplier supplies a specified second
internal resistance detection current different from the first
internal resistance detection current by a difference between the
first internal resistance detection current and the second internal
resistance detection current.
According to this construction, the internal resistance is
calculated by dividing the difference between the terminal voltage
detected by the voltage detector when the first internal resistance
detection current is supplied to the secondary battery and the
terminal voltage detected by the voltage detector when the second
internal resistance detection current is supplied to the secondary
battery by the difference between the first internal resistance
detection current and the second internal resistance detection
current. Thus, the internal resistance of the secondary battery
actually used can be obtained, and the actual value of the internal
resistance can be obtained even if the internal resistance changes,
for example, due to the deterioration of the secondary battery.
Further, it is preferable that a state of charge detector for
detecting a state of charge SOC of the secondary battery and a
storage for storing the state of charge SOC of the secondary
battery and the resistance value of the internal resistance in
correspondence with each other are further provided; and that the
internal resistance detector obtains the resistance value stored in
the storage in correspondence with the state of charge SOC of the
secondary battery detected by the state of charge detector as the
resistance value of the internal resistance of the secondary
battery.
According to this construction, the internal resistance detector
can obtain the resistance value stored in the storage in
correspondence with the state of charge SOC of the secondary
battery detected by the state of charge detector as the internal
resistance of the secondary battery by storing the state of charge
SOC of the secondary battery and the internal resistance in
correspondence beforehand. Thus, in order to obtain the internal
resistance of the secondary battery, it is not necessary to obtain
an open circuit voltage by zeroing the current supply to the
secondary battery and obtaining the terminal voltage by means of
the voltage detector. Therefore, the internal resistance can be
detected by a simple processing.
It is also preferable to further comprise a voltage detector for
detecting the terminal voltage of the secondary battery; and a
constant voltage charging section for causing the charging current
supplier to supply a current for the charging so that, when the
terminal voltage detected by the voltage detector increases to or
above a preset final voltage, the secondary battery is charged with
a constant voltage through the application of the final
voltage.
According to this construction, the terminal voltage of the
secondary battery increases by the supply of the current for the
charging by the charging current supplier and, when the preset
final voltage is reached, it is applied to the secondary battery to
charge the secondary battery with the constant voltage. Then, as
the charging of the secondary battery proceeds, the charging
current of the secondary battery decreases. Therefore, a likelihood
of overcharging the secondary battery can be reduced.
A charging device according to another aspect of the present
invention comprises a connection terminal for the connection with a
secondary battery; a charging current supplier for supplying a
current for charging the secondary battery to the connection
terminal; an internal resistance detector for detecting the
resistance value of the internal resistance of the secondary
battery connected with the connection terminal; and a charge
controller for increasing the current to be supplied to the
connection terminal by the charging current supplier as the
resistance value detected by the internal resistance detector
decreases.
According to this construction, the charging current is increased
as the internal resistance of the secondary battery connected with
the connection terminal decreases while being decreased as the
internal resistance increases. Then, if the internal resistance of
the secondary battery is large as at an initial stage of the
charging, the charging current is decreased to reduce a voltage
drop and self heat generation caused by the internal resistance of
the secondary battery, with the result that a likeliness of
deteriorating the secondary battery due to the internal resistance
of the secondary battery can be reduced. Further, since the
charging current can be increased as the charging proceeds to
decrease the internal resistance, it becomes easier to suppress the
extension of the charging time and shorten the charging time by
increasing the charging current.
A battery pack according to still another aspect of the present
invention is a battery pack connected with a charging device for
outputting a current for charging a secondary battery in response
to an external instruction and comprising a secondary battery; an
internal resistance detector for detecting the resistance value of
the internal resistance of the secondary battery; and a charge
controller for charging the secondary battery by outputting an
instruction to the charging device so that a current to be supplied
to the secondary battery by the charging device is increased as the
resistance value detected by the internal resistance detector
decreases.
According to this construction, in response to the instruction from
the charge controller, the charging device increases the charging
current as the internal resistance of the secondary battery
decreases while decreasing the charging current as the internal
resistance increases. Then, if the internal resistance of the
secondary battery is large as at an initial stage of the charging,
the charging current is decreased to reduce a voltage drop and self
heat generation caused by the internal resistance of the secondary
battery, with the result that a likeliness of deteriorating the
secondary battery due to the internal resistance of the secondary
battery can be reduced. Further, since the charging current can be
increased as the charging proceeds to decrease the internal
resistance, it becomes easier to suppress the extension of the
charging time and shorten the charging time by increasing the
charging current. In this case, it is sufficient for the charging
device to output the current in response to the instruction from
the battery pack, the same charging device can be used even in the
case of charging a battery pack including a secondary battery
having different characteristics.
The charging system, charging device and battery pack according to
the aspects of the present invention can be suitably applicable as
charging systems and battery packs used in battery-driven
apparatuses including electronic equipments such as portable
personal computers and digital cameras and vehicles such as
electric cars and hybrid cars, and as charging devices for charging
secondary batteries.
This application is based on Japanese Patent application serial No.
2006-322141 filed in Japan Patent Office on Nov. 29, 2006, the
contents of which are hereby incorporated by reference.
As this invention may be embodied in several forms without
departing from the spirit of essential characteristics thereof, the
present embodiment is therefore illustrative and not restrictive,
since the scope of the invention is defined by the appended claims
rather than by the description preceding them, and all changes that
fall within metes and bounds of the claims, or equivalence of such
metes and bounds are therefore intended to embraced by the
claims.
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